Opened 2 years ago
Last modified 2 months ago
#33735 closed New feature
Add asynchronous responses for use with an ASGI server — at Version 3
Reported by: | florianvazelle | Owned by: | nobody |
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Component: | HTTP handling | Version: | 4.0 |
Severity: | Normal | Keywords: | ASGI async |
Cc: | Carlton Gibson, Andrew Godwin, Michael Brown, Jon Janzen, Carles Pina Estany | Triage Stage: | Ready for checkin |
Has patch: | yes | Needs documentation: | no |
Needs tests: | no | Patch needs improvement: | no |
Easy pickings: | no | UI/UX: | no |
Description (last modified by )
This ticket follows the one I opened on django/daphne#413.
Initial Issue
Using Daphne as a server for a Django application seems to cause a malfunction in streaming responses.
When you pass an iterator into a response, the contents of the response are not retrieved chunk by chunk, but from a single block when the iterator has finished iterating.
I have a minimal project that can reproduce the behavior, at florianvazelle/minimal-daphne-stream.
Solution
After some research, in Daphne, we use Twisted with asyncioreactor. I managed to reproduce the bug in a minimal way: Minimal example of an "ASGI-like" streaming server with Twisted.
The streaming issue occurs when we call a blocking method in an iterator (io, sleep, request ...), which blocks the reactor. That's why the result is not done progressively.
The reactor does not get control of execution back until the end of the iteration.
To correct this behavior we need to add an asynchronous layer and use async / non-blocking alternatives.
Proposition
In my minimal project, the view will become:
import asyncio from django.http.response import StreamingHttpResponse async def iterable_content(): for _ in range(5): await asyncio.sleep(1) print('Returning chunk') yield b'a' * 10000 def test_stream_view(request): return StreamingHttpResponse(iterable_content())
But django does not handle asynchronous generators.
Some works are already did in this tickets #32798 (StreamingHttpResponse Raises SynchronousOnlyOperation in ASGI Server) – Django, but considering the performance, we could manage it differently here.
I propose to add asynchronous responses, to be used in an async context, so with an ASGI server.
I make a PoC, in a very basic way: PoC Fixed #33735 -- Handle async streaming response.
Change History (3)
comment:1 by , 2 years ago
Description: | modified (diff) |
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comment:2 by , 2 years ago
Cc: | added |
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comment:3 by , 2 years ago
Description: | modified (diff) |
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